CONCRETE RHEOLOGY: WHAT IS IT AND WHY DO WE NEED IT?

摘要

The design of concrete with specified properties for an application is not a new science,but it has taken on a new meaning with the wide use of self compacting concrete(SCC).In this industry,general terms such as "flow under its own weight" and "filling capacity",or workability,flowability,compactibility,stability,finishability,pumpability,and/or consistency are currently used interchangeably without a definition based on fundamental measurements of properties.Several attempts have been made to better relate fresh concrete properties with measurable quantities.Some researchers treated fresh concrete as a fluid and used fluid rheology methods to describe concrete flow.This approach,the most fundamental one,is reviewed in this paper.The main topics that will be addressed are: 1)Review the fundamental definitions of quantities used to uniquely describe the flow of concrete; 2)Give an overview of the tests that are commonly used to measure the rheology of fresh concrete,partially based also on the completed comparison of concrete rheometers sponsored by ACI; 3)Describe methods to predict the flow of concrete from either composition or laboratory tests,including some simulation techniques developed at NIST.A conclusion will present some thoughts on research needed to design SCC with the flow properties required for a given application.